Engine exhaust gas reactors and methods

Abstract

Particulate pollutants such as carbonaceous particles are removed from an engine exhaust stream by passing the exhaust stream through an exhaust gas reactor, the exhaust stream first traversing a charging zone wherein the particles are charged via a corona discharge, and thereafter traversing a downstream collection zone wherein the charged particles are collected and eliminated by a collector/reactor having an oppositely charged reactive collecting surface.

1. A method of removing particles from an engine exhaust stream, the method comprising:
 passing an engine exhaust stream carrying suspended carbonaceous particles into a charging zone in an exhaust passageway; 
 providing an assembly having at least one internal surface defining the exhaust passageway, the assembly including a first electrode least partially disposed in an upstream portion of the exhaust passageway forming the charging zone, and a particulate collector supporting the oppositely charged collecting surface at least partially disposed in a downstream portion of the exhaust passageway forming the collection zone; 
 generating a corona discharge in the charging zone from the first electrode effective to produce at least some charged carbonaceous particles; 
 applying an electrical potential to the particulate collector that is sufficient to cause at least some of the charged carbonaceous particles to be deposited on the collecting surface; 
 passing the exhaust stream and charged carbonaceous particles from the charging zone into a collection zone downstream of the charging zone in the exhaust passageway; 
 electrostatically attracting at least some of the charged carbonaceous particles to an oppositely charged collecting surface within the collection zone; and 
 allowing the exhaust stream exclusive of the particles deposited on the collecting surface to exit the exhaust passageway; 
 wherein the collecting surface comprises a catalyst, and wherein at least some of the particles deposited on the collecting surface are chemically reacted upon contact with the collecting surface. 
 
     
     
       2. The method of  claim 1  wherein the particles deposited on the collecting surface are catalytically reacted to form carbon dioxide and water. 
     
     
       3. The method of  claim 1  wherein the exhaust stream includes nitrogen oxides and water vapor, and wherein the catalyst supports reactions among the nitrogen oxides, the water vapor, and the carbonaceous particles. 
     
     
       4. The method of  claim 1  wherein the temperature of the exhaust stream is sufficient to support catalytic reactions including reductions of nitrogen oxides to diatomic nitrogen. 
     
     
       5. The method of  claim 1  wherein the exhaust stream is an exhaust stream from a direct injection gasoline engine, and wherein the carbonaceous particles include particles below 1 μm in size. 
     
     
       6. The method of  claim 1  wherein the step of passing the exhaust stream and charged carbonaceous particles from the charging zone into the collection zone is carried out while electrically isolating the collection zone from the charging zone. 
     
     
       7. The method of  claim 6  wherein substantially all of the suspended carbonaceous particles are transported through the charging zone without deposition on exhaust passageway surfaces within the charging zone. 
     
     
       8. The method of  claim 1  wherein the exhaust stream is split into a plurality of sub-streams within the particulate collector. 
     
     
       9. An electrostatic exhaust particulate reactor comprising:
 an assembly incorporating at least one internal surface defining an exhaust passageway, the passageway having an upstream portion extending away from an exhaust inlet port and a downstream portion connecting with the upstream portion and terminating at an exhaust outlet port; 
 a charging section within the upstream portion including a first electrode for generating a corona discharge; 
 a collection section within the downstream portion including a particulate collector/reactor having a charged collecting surface for collecting carbonaceous particles, wherein the charged collecting surface comprises a catalyst; 
 one or more sources of electrical potential connecting with the first electrode and with the charged collecting surface for electrically charging the electrode and collecting surface. 
 
     
     
       10. The reactor of  claim 9  wherein the charging section further comprises a second electrode in opposition to the first electrode, the second electrode being maintained at a neutral electrical potential and the first electrode being maintained at an electrical potential sufficient to positively charge at least some carbonaceous particles transiting the charging section. 
     
     
       11. The reactor of  claim 9  wherein the charging section is electrically isolated from the collection section. 
     
     
       12. The reactor of  claim 9  wherein the catalyst is active for the oxidation of carbonaceous particles supported on the charged collecting surface in the presence of nitrogen oxides and/or water vapor. 
     
     
       13. The reactor of  claim 9  wherein the particulate collector/reactor comprises a plurality of interconnecting walls supporting catalyst coatings and defining a plurality of mutually parallel channels extending in a direction generally parallel with the exhaust passageway. 
     
     
       14. The reactor of  claim 13  wherein the particulate collector/reactor comprises a matrix comprised of longitudinally extending transverse members. 
     
     
       15. The reactor of  claim 13  wherein the collector/reactor is comprised of metal. 
     
     
       16. The reactor of  claim 13  wherein the collector/reactor is comprised of metallized ceramic. 
     
     
       17. The reactor of  claim 13  wherein the catalyst has a composition effective to promote at least one reaction selected from the group consisting of the following reactions:
   C( s )+2H 2 O( g )→CO 2 ( g )+2H 2 ( g ),
 
   2C( s )+2H 2 O( g )→CO 2 ( g )+CH 4 ( g ),
 
   C( s )+H 2 O( g )→CO( g )+H 2 ( g ),
 
   C( s )+CO 2 ( g )→2CO( g ),
 
   2NO 2 ( g )+CH 4 ( g )→N 2 ( g )+CO 2 ( g )+2H 2 O( g ), and
 
   2NO( g )+2CO( g )→N 2 ( g )+2CO 2 ( g ).